The Reality of Suffering--dukkha

The Pali word dukkha, in ordinary usage means 'suffering', 'pain',
'sorrow' or 'misery'. But in the context of the First Noble Truth,
dukkha also means 'imperfection', 'impermanence', 'emptiness',
'insubstantiality'.
There are three kinds of suffering:

There are all kinds of suffering in life: birth, old age, sickness, death,
association with unpleasant persons and conditions, separation from beloved
ones and pleasant conditions, not getting what one desires, grief, lamentation,
distress--all forms of physical and mental suffering.

Pleasant and happy feelings or conditions in life are not permanent.
Sooner or later they change. When they change they may produce pain,
suffering, unhappiness or dissappointment. This vicissitude is considered
viparimana-dukkha.

An 'individual', an 'I' or a 'self' is a combination of ever-changing mental
and physical forces which can be divided into five groups or 'aggregates'
pancakkhandha. Suffering as conditioned states is produced by
attachment to these five aggregates: